1. Field of the Invention
The present invention relates to a plasma treating apparatus, particularly, to a plasma treating apparatus with an improved supply mechanism of a high frequency power.
2. Description of the Related Art
A plasma treating apparatus, e.g., a plasma etching apparatus, comprises a chamber maintained at a vacuum and kept at the ground potential, a susceptor arranged within the chamber and supplied with a high frequency power, the susceptor being electrically insulated from the chamber, an electrostatic chuck arranged on the susceptor for fixing a workpiece, e.g., a semiconductor wafer, within the chamber, an exhaust means for discharging a gas from within the chamber, and a supply means for supplying a reacting gas for the etching into the chamber.
Proposed is an electrostatic chuck of monopole type constructed such that an electrically conductive layer is formed within an insulating layer. The electrostatic chuck of this construction permits fixing a workpiece (wafer) as follows. Specifically, if a high frequency power is supplied to the susceptor, plasma is generated between the susceptor and the chamber of the ground potential, which faces the susceptor, with the result that the ions contained in the plasma permit the wafer disposed on the electrostatic chuck to bear the ground potential. If a high voltage is applied under this condition to the conductive layer included in the electrostatic chuck, Coulomb attraction is generated between the conductive layer of the chuck and the wafer kept at the ground potential, i.e., the wafer disposed on the insulating layer of the chuck. As a result, the wafer is electrostatically sucked so as to be fixed to the insulating layer of the electrostatic chuck. It follows that the plasma etching apparatus of the construction described above necessitates a cable for applying a high voltage to the conductive layer of the electrostatic chuck and a means for supplying a high frequency power to the susceptor.
Where the electrostatic chuck is arranged on the susceptor, the conductive layer of the chuck is positioned to face the susceptor with the insulating layer of the chuck interposed therebetween, with the result that a capacitor of a large area is formed between the susceptor and the conductive layer of the electrostatic chuck. What should be noted is that, if a high frequency power is supplied to the susceptor, the capacitor noted above forms a path of the high frequency power. In other words, the high frequency power (RF current) supplied to the susceptor flows into the conductive layer of the electrostatic chuck through the capacitor. The RF current further flows from the conductive layer into the cable connected thereto, giving rise to the problem that the cable acts as an antenna for scattering the RF current. To be more specific, the cable is coupled with a member of the ground potential, e.g., chamber, positioned in the vicinity of the cable so as to form a capacitor and, thus, to bring about RF current leakage.
What should also be noted is that the RF current flowing into the conductive layer of the electrostatic chuck breaks down the insulating film positioned between the conductive layer and the susceptor, leading to a short-circuiting between the conductive layer and the susceptor.
To reiterate, the problems noted above are brought about in the case of using an electrostatic chuck of a monopole type construction. In addition, similar problems are brought about in the case of using an electrostatic chuck of other constructions including, for example, an electrostatic chuck of a dipole type in which two conductive layers, which are electrically insulated from each other, are arranged with an insulating layer interposed therebetween, positive and negative voltages being applied to these two conductive layers, respectively, and an electrostatic chuck of a tetrapole type in which four conductive layers, which are electrically insulated from each other, are arranged with an insulating layer interposed between adjacent conductive layers, positive voltage being applied to two of the four conductive layers and negative voltage being applied to the other two conductive layers.